1. Field of the Invention
This invention relates to an apparatus for unloading particulate material from ships.
More specifically, the invention relates to a simple economical method of converting a standard Great Lakes bulk carrying ship into a vessel capable of discharging grain or other free flowing cargoes to a shore-based hopper or pile.
2. Description of the Prior Art
The bulk of grain is unloaded world-wide from vessels by shore-based equipment in the form of bucket elevator legs, vacuum hoses, screw elevators, en masse elevators and other devices. This shore-based equipment is generally costly to install, maintain and also operate. Shore-based grain elevators with significant flowthrough tonnages can justify the expenditure and operating costs of the required unloading equipment, but grain elevators with smaller requirements tend to attract vessels capable of discharging the grain with ship board equipment.
There are numerous ships trading both on the ocean and within the Great Lakes system which can self-charge by one method or another and there is a trend to have more of these vessels deliver grain to ports having smaller grain elevators without proper unloading facilities.
These self-unloading vessels are generally designed to carry a wide variety of different cargoes and tend to be more sophisticated than is required for many of the grain trades.
Self-unloaders fall into several categories, including gravity type which has hopper shaped holds with bottom feeding to two or more fore and aft conveyor belts which in turn feed an elevating device which feeds a long conveyor boom for shore delivery. Another is the reclaimer type which has a large material reclaiming device in the hold which feeds a fore and aft conveyor belt situated below the tank top or bottom of the hold. This conveyor belt feeds the elevating device in a similar fashion to the gravity-type described above.
Various other systems have been developed over the years which discharge the cargo through the hatch openings on deck. These have taken the form of bucket elevators, screw conveyors, grab buckets and the like. These devices have tended to be heavy, expensive and elaborate. In cases where an elevating leg enters the hold to retrieve particulate cargo, the leg moves along a vertical axis requiring a substantial supporting structure to retain stability when the vertical leg is extended above deck. The majority of the shipboard unloading systems which have been developed to date, while suitable for unloading grain or other free flowing cargoes suffer from their physical size, weight and high cost.
The present design of a Great Lakes vessel has evolved over the years to suit the particular trading patterns and the restrictions of these waters including navigation in the St. Lawrence Seaway system. The vessels have a length of between 700 ft. and 1000 ft. and a beam of between 70 ft. and 105 ft. The depth of the vessels vary between 40 ft. and 50 ft. and all have decks clear of obstruction to facilitate easy loading and unloading.
A typical Seaway size lake vessel will have a length of 730 ft., a beam of 75 ft., and a depth of 40 ft. The cargo space length will be about 550 ft. which is usually divided fore and aft by bulkheads into, approximately five holds each of about 110 ft. in length. There are generally a number of single piece hatch covers on the deck above each hold to allow for loading and unloading. These covers measure about 50 ft. athwartships and about 15 ft. in the fore and aft direction. The single-piece hatch covers are clamped to the raised hatch coamings around the hatch openings when the vessel is at sea and are removed in port by a hatch crane prior to loading or unloading. The hatch crane is a steel bridge which straddles the hatch covers in an athwartships direction and is mounted on rail tracks which run in a fore and aft direction for the entire length of the open deck. The rails are positioned outboard of the hatch coamings and between these coamings and the ship's side. Power driven winches are located on the heavy athwartships beams of the hatch crane and these are used to lift the covers on or off as required. The hatch crane bridge is powered to travel in the fore and aft direction on the rails which is necessary in order to place the covers in a storage location.
The present invention is particularly applicable to vessels designed for and trading within the North American Great Lakes system including the St Lawrence Seaway. It primarily addresses modifications which can be affected to existing vessels, but the system could also be built into new vessels.
It is an aim of this invention to introduce an unloading system which takes advantage of certain characteristics of "Lake" style vessels and also uses equipment already installed on board.
The invention takes advantage of the long unobstructed deck of a "Lake" vessel, and the hatch crane bridge described above or, another similar type bridge equipped for the intended purpose. It also utilizes the rail tracks which carry the deck crane.
The system is tailored to the receiving capabilities of the smaller grain elevators and is light in weight. The installation of the unloading system would not detract from the capabilities of the vessel when trading as a standard bulk carrier and, as no cargo hold hoppers are required, it would not reduce the cargo hold volume which would affect the earning capacity of the vessel.
A construction in accordance with the present invention for unloading particulate material from the elongated hold of a ship having a deck provided with a number of athwartship elongated hatches leading to the hold spaced apart in the fore and aft direction, comprises a mounting means above the deck for movement in the athwartships direction and in the fore and aft direction. An unloading leg in the form of a continuous conveyor means having a discharge end and a distal end is provided which can pivot on the mounting means. The discharge end of the conveyor means is pivotally mounted to the mounting means for pivotal movement of the leg about a horizontal pivot axis in an athwartship plane from a rest position above the deck to a vertical position with the distal end near the bottom of the hold. Means are provided for raising and lowering the distal end of the conveyor means into the hold by pivoting the unloading leg about the pivot axis of the conveyor means. Means are provided for receiving material from the discharge end of the conveyor means and conveying it outboard of the ship.
A specific embodiment of the present invention includes an unloading system which comprises a marine grain leg pivoted by a pivot shaft to a carriage mounted through drive wheels on rail tracks on an unloading bridge. A winch mounted on the bridge is used to raise or lower the working end of the leg with a luffing cable to reach the grain in the cargo hold. A transfer conveyor belt adjacent to the marine leg runs in an athwartship direction on the bridge. A transfer chute to direct the grain to a fore and aft conveyor belt which is installed parallel to the deck rails and over the entire length of the open deck. At the forward or after end of the vessel, a system of transfer and elevating equipment i used to feed the grain to an unloading boom to carry the grain to the elevator.